Directory UMM :Data Elmu:jurnal:A:Applied Soil Ecology:Vol12.Issue3.Jul1999:
Applied Soil Ecology 12 (1999) 263±272
Field and laboratory evaluation of soil quality changes resulting
from injection of liquid sewage sludge
S. Stamatiadisa,*, J.W. Doran1,b, T. Kettler2,c
a
Goulandris Natural History Museum, Ecology-Biotechnology Laboratory, 13 Levidou Street, 145 62 Ki®ssia, Greece
b
USDA-ARS, 116 Keim Hall, University of Nebraska, Lincoln, NE 68583, USA
c
USDA-ARS, 116 Keim Hall, University of Nebraska, Lincoln, NE 68583, USA
Received 21 January 1998; accepted 17 December 1998
Abstract
Soil quality changes resulting from repeated or single injection of liquid municipal sewage sludge were evaluated in terraced
cropland in eastern Nebraska, USA. Differences in soil properties among sampling locations were explained primarily by two
factors, landscape position and sludge injection. Selected chemical properties (pH, EC, NO3±N) did not generally differ
between landscape positions, but soil organic matter (organic C and N) and microbial activity indices (soil respiration,
biomass N, available N, mineralization and nitri®cation rates) were more sensitive indicators of change. Values of these
indicators generally increased down-slope from the upper terrace to the grassed waterway on a west facing slope. A probable
similar pattern on the east slope was obscured by repeated application of sludge. Single or repeated (long-term) sludge
injection increased the readily decomposable organic matter, ammonium- and available-N in soil (0±30.5 cm depth). These
changes stimulated soil microbial activity as evidenced by increased basal respiration, net mineralization and nitri®cation
rates. Consequently, nitri®cation of ammonium-N was re¯ected in soil chemical properties as increased soil nitrate-N (to
levels that were more than two times higher than suf®ciency levels for corn) and EC and by decreased pH. In-®eld
measurements detected changes in physical properties such as a decrease of in®ltration rate caused by sludge injection and soil
compaction as a result of traf®c operations. Differences between the sites of single and repeated sludge injection were found in
soil pH, ammonium-N, organic matter and microbial activity. Recent sludge injection resulted in higher ammonium-N
concentration and higher microbial activity in soil, and repeated sludge injection resulted in lower pH and in greater organic
matter content. Regardless of these differences in soil properties between the sites of single and repeated sludge application,
the overall changes that were caused by sludge injection had both positive and negative effects on soil quality and the
sustainability of this management practice. Increase of organic matter content and biological activity improved soil fertility,
but excessive amounts of ammonium salts contained in liquid sludge resulted in soil nitri®cation, excessive nitrate formation
and acidi®cation. These processes reduce soil productivity, increase the risk of ground- and surface-water contamination and
pose a threat to plant and animal health. # 1999 Elsevier Science B.V. All rights reserved.
Keywords: Environmental quality; Landscape position; Nitri®cation; Acidi®cation; Microbial activity; Indicators; Physical properties
*Corresponding author. Tel.: +30-1-8087345; fax: +30-1-8080674.
Tel.: +1-402-4721510; fax: +1-402-4720516.
2
Tel.: +1-402-4721510; fax: +1-402-4720516.
1
0929-1393/99/$ ± see front matter # 1999 Elsevier Science B.V. All rights reserved.
PII: S 0 9 2 9 - 1 3 9 3 ( 9 9 ) 0 0 0 0 7 - 4
264
S. Stamatiadis et al. / Applied Soil Ecology 12 (1999) 263±272
1. Introduction
The application of domestic sewage sludge to agricultural land has become an acceptable method of
waste disposal and soil amendment. A great number of
studies have been published which document the
effects of sludge application on soil properties, nutrient availability and crop growth, heavy metal toxicity,
degradation of organic pollutants, and contamination
of surface and ground water. Studies of soil property
changes have selectively focused on nutrient enrichment and de®ciency, organic matter dynamics, chemical toxicities, microbial and enzymatic activity and
soil physical parameters (Metzger and Yaron, 1987;
Smith, 1991; Berti and Jacobs, 1996; Smith, 1996;
McBride et al., 1997). Sewage sludge application to
soil generally improves soil fertility by increasing the
soil organic matter, microbial activity and residual
nitrogen and by improving soil physical properties.
Reduced bulk density and increased porosity,
improved aggregate stability and enrichment of soil
organic carbon result generally in increased water
retention capacity and available water in coarse-textured soils and, in the long-term, in enhanced water
transmission properties as de®ned by improved
hydraulic conductivity and increased in®ltration.
However, it is necessary to apply sludge at large rates,
exceeding the maximum recommended level of N
application in manures, or at repeated low levels in
order to gain a signi®cant improvement of soil physical properties (Hall and Coker, 1983; Metzger and
Yaron, 1987; Smith, 1996). It is these high rates of
application that exceed crop N requirements which
may cause undesirable changes in soil chemical properties such as excessive soil acidi®cation from nitri®cation of the added ammonia, accumulation of
nitrates in sludge-treated pro®les and increased nitrate
leaching from susceptible loamy soils (Bergstrom and
Brink, 1986; Speirs and Frost, 1987; Chang et al.,
1988; Jansson et al., 1989; Powlesland and Frost,
1990).
Recent efforts for integrated soil quality assessment
recognize the need for reliable indicators of soil
productivity, environmental quality and plant/animal
health. In this study, a combination of physical, chemical and biological soil properties were used for the
evaluation of soil quality changes as a result of single
and repeated injection of liquid digested sludge in an
agricultural soil. The selected measurements comply
with the proposed selection criteria of soil quality
indicators in that they are sensitive to variations in
management, they de®ne major ecological processes
in soil and they re¯ect conditions as they actually exist
in the ®eld under a given management system (Doran
et al., 1996). Soil injection of sludge is widely practiced and signi®cantly reduces ammonia loss by volatilization, but leads to increased leaching of N as
compared to surface application (Williams and Hall,
1986; Smith, 1996). In this case, sludge was injected to
shallow depth for close proximity to crop roots in the
fall in order to minimize leaching losses (Shepherd,
1992; Smith, 1996). The speci®c objectives of this
study were the assessment of soil quality changes
caused by (a) repeated (long-term) liquid sludge injection at cumulative loadings that correspond to the
maximum annual recommended level of N application
in organic manures, (b) single sludge injection at rates
exceeding the maximum annual recommended level
of N application and (c) landscape position as compared to sludge injection effects.
2. Methods
2.1. Site description and sludge application
The experimental site is located in Lancaster county
NE, north of the city of Lincoln, NE, and is a terraced
dryland of east and west facing slopes meeting in a
grass waterway. Each slope was composed of an upper
and a lower terrace which, together with the waterway,
resulted in ®ve different sampling locations. The soil
type was Sharpsburg silty clay loam (®ne, montmorillonitic, mesic Typic Argiudoll).
The upper East terrace received anaerobicallydigested liquid sewage sludge from the NE Lincoln
sewage treatment plant by injection every three years
since 1982 at an estimated cumulative loading of
52 Mg haÿ1 of dry solids (ds) over a 12-year-period
for an average of 10.4 Mg ds haÿ1 (674 kg N haÿ1)
per injection which corresponds to 3.5 Mg ds haÿ1
yearÿ1 (225 kg N haÿ1 yearÿ1). In terms of N, this
is close to the maximum annual rate that is recommended for the application of organic manures (CEC,
1991; MAFF, 1991) in order to control nitrate contamination of groundwater in potentially susceptible
265
S. Stamatiadis et al. / Applied Soil Ecology 12 (1999) 263±272
areas. The site was cultivated to wheat without inorganic fertilizers in order to reduce excessive soil
nutrient loadings, the herbicide Roundup was used
to kill the wheat and the soil was disc-tilled prior to
sludge application. In addition, a 3.9-acre section of
the lower East terrace was reported to have received
458,514 L of sewage sludge (2.9% dry matter content,
8.4 Mg ds haÿ1 or 608 kg N haÿ1) for the ®rst time on
30 August, 1995. In terms of N, this rate is three times
higher than the recommended maximum annual application rate of organic manures (CEC, 1991; MAFF,
1991), but in terms of organic solids it is three times
lower than the suggested rates for a signi®cant
improvement of soil quality with respect to soil physical properties and organic matter content in sandy
loam soils (Smith, 1996). The sludge was applied by
injection to a depth of 20 cm below the soil surface in
rows of ca. 64 cm apart by a caterpillar track vehicle.
The chemical characteristics of the applied sludge are
presented in Table 1.
2.2. Soil sampling and analysis
An overview of the sampling scheme is given in
Table 2. Five random composite samples (0±30.5 cm
depth) were taken with a step-down Oak®eld probe
from each landscape position on 29 August and from
sludge application (row) and non-application (interrow) zones of the lower east terrace on 14 September,
1995. After mixing in a bucket, the samples were
sealed in plastic bags, placed in a portable cooler and
taken to the laboratory. Samples were sieved through a
2 mm sieve at ®eld moisture content prior to analysis.
Standard laboratory analysis of physical and chemical
properties of composite soil samples included gravimetric water content, bulk density (BD), nitrate and
ammonium nitrogen by extraction with 2 M KCl and
colorimetric determination with a ¯ow injection analyzer (Keeney and Nelson, 1982) followed by adjustment for 1 : 1 soil-water mixture from air-dried soil,
pH and electrical conductivity (EC) adjusted for 1 : 1
soil-water mixture, total C and N by dry combustion of
samples in an elemental analyzer (Schepers et al.,
1989), potentially mineralizable N (available N) by
the quantity of ammonium-N produced during incubation of soil samples for 1 week at 408C under
waterlogged conditions (Keeney, 1982). Measured
soil biological properties included basal soil respira-
Table 1
Chemical composition of liquid sewage sludge (pH 7) injected in
1.6 ha of the lower east terrace on 30 August, 1995
Component
Reported concentration
mg kgÿ1
dry kg haÿ1a
Total solids
Volatile solids
28900
15850
8398
4606
Total Nitrogen
Organic N
Ammonium N
Nitrate N
72457
45730
26740
6.8
Phosphorus
Sulfate
Iron
Potassium
10435
6207
11768
6290
Heavy metals and other
Arsenic
Cadmium
Chromium
Copper
Lead
Manganese
Mercury
Molybdenum
Nickel
Selenium
Silver
Zinc
9.6
5.9
43.4
1163
222
487
4.6
59.8
65.5
1.5
59.2
2292
608
384
224
0.06
88
52
99
53
0.08
0.05
0.36
9.8
1.9
4.1
0.04
0.50
0.55
0.01
0.50
19.25
a
Assuming 2.9% dry matter content and 290 538 L haÿ1 as the
reported sludge application rate.
tion by gas chromatographic analysis of headspace
CO2 after aerobic incubation of samples in sealed
1.9 L jars, net mineralization/ nitri®cation rates after
analysis of the incubated samples for ammonium- and
nitrate-N, biomass C by gas chromatographic analysis
of headspace CO2 of untreated and fumigated samples
with chloroform and biomass N by determination of
mineral nitrogen of the same samples. For the estimation of basal soil respiration, soil biomass, net mineralization and nitri®cation, non-fumigated soil samples
were incubated at 55% water-®lled pore space and
258C for 20 days. Biomass C and N was determined by
the fumigation/incubation method of Jenkinson as
described by Rice et al. (1996).
Replicated surface soil samples (0±7.6 cm depth)
were also taken from the lower east terrace on 14±15
266
S. Stamatiadis et al. / Applied Soil Ecology 12 (1999) 263±272
Table 2
The soil sampling scheme (site, sampling depth, date) of the experimental area in order to test the effects of landscape position and sludge
injection
Site
Sludge injection
Sampling depth (cm) and site selection to test effect of
Landscape position
Repeated injection
29 August
Grass waterway
West upper terrace
West lower terrace
East upper terrace
East lower terrace
No
No
No
Repeated
No
No (inter-row)
Single (row)
30.5
30.5
30.5
30.5
September, 1995, 2 weeks after sludge injection. Soil
samples were collected with aluminium sampling
tubes (7.4 cm inside diam.) from three consecutive
rows and inter-rows in a perpendicular line so that the
distance between two consecutive samples was 32 cm.
Three additional top soil samples were taken from the
adjacent part of the terrace which had not been subjected to sludge injection (control samples). These
samples were analyzed for gravimetric water content,
bulk density, electrical conductivity, nitrate-N and pH
in the laboratory as described above. On-site water
in®ltration rate was measured within aluminum in®ltration rings (15 cm inside diameter) which were
inserted to a 7.6 cm soil depth. Soil respiration
(pre- and post-irrigation) was measured from the
headspace of in®ltration rings covered for 30 min
using Draeger tubes. Post-irrigation top soil samples
from within the irrigation rings were taken with the
sampling tubes and analyzed for soil bulk density and
water holding capacity (WHC). Further details of the
®eld soil quality procedures used are given by Sarrantonio et al. (1996).
2.3. Statistical analysis
Analysis of variance (ANOVA) was performed on
data obtained from replicated surface soil samples.
Sludge treatment was the independent factor of the
model in a completely randomized design. Neuman±
Keuls post hoc comparison of means was used at the
level of p < 0.05. Correlation coef®cients were computed between all microbial indices measured for 0±
30.5 cm depth by standard analytical procedures. All
Single injection
14 September
30.5
30.5
30.5
30.5
7.6
7.6/30.5
7.6/30.5
the employed procedures are reported in StatSoft
(1995).
3. Results and discussion
Bulk density, electrical conductivity, pH, nitrate and
ammonium N of the initial deeper soil samples (0±
30 cm) were similar in all terraces except those of the
upper east terrace which had repeatedly received
sludge since 1982. The upper east terrace had higher
soil conductivity, nitrate and ammonium levels and
lower pH than the other terraces (Table 3). Electrical
conductivity was positively related to nitrate concentration in all landscape positions except the waterway
(Table 3). Elemental analysis and anaerobic N mineralization showed a progressive increase of total C and
N and available N down the slope of the west side to
the waterway (Table 3). With the exception of biological indices involving microbial C, all other indices
of microbial activity followed a similar increasing
trend with lowest values in the upper west terrace.
Basal soil respiration, biomass N and its proportion to
total N (Nb : Nt) had the highest values in the grassed
waterway, the last two indices having values at least
two times higher than those of the west terraces. This
progressive increase in soil fertility was probably
caused by lateral leaching and surface erosion from
higher elevations. A possible similar pattern on the
east slope was obscured, and reversed, by sludge
application in the upper east terrace. Total C and N,
N availability and all biological indices had higher
values in the upper than the lower east terrace due to
267
S. Stamatiadis et al. / Applied Soil Ecology 12 (1999) 263±272
Table 3
Soil quality changes as a result of landscape position and repeated sludge application
Soil quality indicator
Water-way
(grass)
Terrace position
Lower west
Upper west
Lower east
Upper easta
Physical
Soil bulk density (g/cm3)
1.38
1.43
1.49
1.42
1.41
Chemical
Soil EC1:1 (dS/m)
Soil pH
Soil NO3±N (kg NO3±N/ha 30.5 cm)
Soil NH4±N (kg NH4±N/ha 30.5 cm)
0.30
6.79
7.1
4.2
0.12
6.46
25.0
4.7
0.16
6.35
18.9
1.0
0.12
6.24
20.2
4.4
0.30
5.96
156.7
20.5
Total C (kg C/ha 30.5 cm)
Total N (kg N/ha 30.5 cm)
C/N Ratio
58467
5817
10.1
37920
4838
7.8
19 529
3 234
6.0
31 163
4 017
7.8
Biological
Biomass C (kg C/ha 30.5 cm)
Biomass N (kg N/ha 30.5 cm)
Biomass C : N
396
126.7
3.1
1299
45.6
28.5
794
43.7
18.2
218
30.6
7.1
Available N (kg NH4-N/ha 30.5 cm)b
Available N: Total C (mg/g)
Available N: Total N (mg/g)
113.2
1.9
19.5
60.0
1.6
12.4
38.4
2.0
11.9
36.4
1.2
9.1
34811
5011
6.9
1476
ÿ66.9e
75.3
2.2
15.0
Net mineralization (kg/ha 30.5 cm/day)
0±10 days
0±20 days
2.32
1.54
2.27
1.59
0.06
0.33
0.75
0.43
ÿ2.30
1.87
Net nitrification (kg/ha 30.5 cm/day)
0±10 days
0±20 days
2.64
1.73
2.67
1.82
0.09
0.37
1.12
0.64
ÿ0.30
2.86
Respiration (kg CO2±C/ha 30.5 cm/day)c
0±10 days
10±20 days
0±20 days
4.76
3.18
3.97
2.71
1.37
2.04
3.19
1.94
2.57
1.76
1.08
1.42
2.81
1.32
2.07
3.4
0.9
1.6
4.1
0.8
3.2
0.7
1.4
6.5
4.2
Biomass C: total C, %
Biomass N: total N, %
Specific respiratory activityd
0.7
2.2
10.0
1.4
a
Injected with sewage sludge every 3 years since 1982.
NH4±N released during anaerobic incubation for 1 week at 408C.
c
2.25 cm depth.
d
qCO2 (mg CO2-C gÿ1 biomass C dayÿ1).
e
Error due to presence of readily decomposable organic material resulting from sludge injection.
Values represent single measurements of composite samples (0.30.5 cm depth, n 5) taken on 29 August, 1995.
b
long-term sludge application (Table 3). The higher
ratio of available N: total C in the soil of repeated
sludge injection is indicative of the presence of readily
decomposable organic material.
The effects of the single sludge injection at the
lower east terrace were similar to those of repeated
sludge injection. The treated soil (sludge rows) had
greater organic matter content, microbial activity,
268
S. Stamatiadis et al. / Applied Soil Ecology 12 (1999) 263±272
Table 4
Effects of recent sludge injection on indicators of soil quality
Soil quality indicator
Area of sludge injection
Application row (sludge)
Physical
Soil bulk density (g/cm3)
Chemical
EC1:1 (dS/m)
Soil pH
Soil NO3±N (kg NO3±N/ha 30.5 cm)
Soil NH4±N (kg NH4±N/ha 30.5 cm)
1.36
1.35
1.0
0.37
6.28
172.2
67.2
0.10
6.71
8.9
3.0
3.7
0.9
19.4
22.4
Total C (kg C/ha 30.5 cm)
Total N (kg N/ha 30.5 cm)
20312
3826
Biological
Biomass C (kg C/ha 30.5 cm)
Biomass N (kg N/ha 30.5 cm)
ÿ205b
ÿ69.0b
Available N (kg NH4±N/ha 30.5 cm)a
Available N: total C (mg/g)
Available N: total N (mg/g)
Net mineralization (kg N/ha 30.5 cm/day)
0±10 days
0±20 days
Inter-row (no-sludge)
Ratio
Sludge/no-sludge
66.5
3.3
17
17282
2724
1.2
1.4
138
22.7
18.0
1.0
7
3.7
3.3
2.4
8.18
8.00
0.29
0.32
28.2
25.0
Net nitrification (kg NO3±N/ha 30.5 cm/day)
0±10 days
0±20 days
14.57
11.26
0.50
0.46
29.1
24.5
Respiration (kg CO2-C/ha 30.5 cm/day)
0±10 days
10±20 days
0±20 days
34.8
36.9
35.9
16.8
12.3
14.6
2.1
3.0
2.5
a
NH4±N released during anaerobic incubation for 1 week at 408C.
Error due to presence of readily decomposable organic material resulting from sludge injection.
Values represent single measurements of composite samples (0±30.5 cm depth, n 5) taken on 14 September, 2 weeks after sludge
application.
b
available N, mineral N and electrical conductivity and
decreased pH relative to the untreated soil of the interrows, 2 weeks after sludge injection (Table 4).
Digested sludge injection at a rate of 608 kg N haÿ1
was three times higher than the recommended maximum application of organic manures (160 or 210 kg
N haÿ1 yearÿ1; CEC, 1991), four times higher than the
range of 100±160 kg N/ha estimated to be the `breakpoint' which prevents nitrate leaching for cereals
(Bergstrom and Brink, 1986; Jansson et al., 1989)
and, based on calculations of Powlesland and Frost
(1990), may be expected to increase groundwater
concentration by approx. 9 ppm NO3-N. Two weeks
after injection, the majority (72%) of the ammoniumN contained in sludge was converted to soil nitrate-N
whose concentration raised to levels that were two
times higher than suf®ciency levels for corn during
early growing season (20±25 ppm, Bundy and Meisinger, 1994, p. 958), which equated to 80±
100 kg haÿ1 in the top 30 cm. Suf®ciency levels for
manured soil are even lower at about 16 ppm or less
that equate to
Field and laboratory evaluation of soil quality changes resulting
from injection of liquid sewage sludge
S. Stamatiadisa,*, J.W. Doran1,b, T. Kettler2,c
a
Goulandris Natural History Museum, Ecology-Biotechnology Laboratory, 13 Levidou Street, 145 62 Ki®ssia, Greece
b
USDA-ARS, 116 Keim Hall, University of Nebraska, Lincoln, NE 68583, USA
c
USDA-ARS, 116 Keim Hall, University of Nebraska, Lincoln, NE 68583, USA
Received 21 January 1998; accepted 17 December 1998
Abstract
Soil quality changes resulting from repeated or single injection of liquid municipal sewage sludge were evaluated in terraced
cropland in eastern Nebraska, USA. Differences in soil properties among sampling locations were explained primarily by two
factors, landscape position and sludge injection. Selected chemical properties (pH, EC, NO3±N) did not generally differ
between landscape positions, but soil organic matter (organic C and N) and microbial activity indices (soil respiration,
biomass N, available N, mineralization and nitri®cation rates) were more sensitive indicators of change. Values of these
indicators generally increased down-slope from the upper terrace to the grassed waterway on a west facing slope. A probable
similar pattern on the east slope was obscured by repeated application of sludge. Single or repeated (long-term) sludge
injection increased the readily decomposable organic matter, ammonium- and available-N in soil (0±30.5 cm depth). These
changes stimulated soil microbial activity as evidenced by increased basal respiration, net mineralization and nitri®cation
rates. Consequently, nitri®cation of ammonium-N was re¯ected in soil chemical properties as increased soil nitrate-N (to
levels that were more than two times higher than suf®ciency levels for corn) and EC and by decreased pH. In-®eld
measurements detected changes in physical properties such as a decrease of in®ltration rate caused by sludge injection and soil
compaction as a result of traf®c operations. Differences between the sites of single and repeated sludge injection were found in
soil pH, ammonium-N, organic matter and microbial activity. Recent sludge injection resulted in higher ammonium-N
concentration and higher microbial activity in soil, and repeated sludge injection resulted in lower pH and in greater organic
matter content. Regardless of these differences in soil properties between the sites of single and repeated sludge application,
the overall changes that were caused by sludge injection had both positive and negative effects on soil quality and the
sustainability of this management practice. Increase of organic matter content and biological activity improved soil fertility,
but excessive amounts of ammonium salts contained in liquid sludge resulted in soil nitri®cation, excessive nitrate formation
and acidi®cation. These processes reduce soil productivity, increase the risk of ground- and surface-water contamination and
pose a threat to plant and animal health. # 1999 Elsevier Science B.V. All rights reserved.
Keywords: Environmental quality; Landscape position; Nitri®cation; Acidi®cation; Microbial activity; Indicators; Physical properties
*Corresponding author. Tel.: +30-1-8087345; fax: +30-1-8080674.
Tel.: +1-402-4721510; fax: +1-402-4720516.
2
Tel.: +1-402-4721510; fax: +1-402-4720516.
1
0929-1393/99/$ ± see front matter # 1999 Elsevier Science B.V. All rights reserved.
PII: S 0 9 2 9 - 1 3 9 3 ( 9 9 ) 0 0 0 0 7 - 4
264
S. Stamatiadis et al. / Applied Soil Ecology 12 (1999) 263±272
1. Introduction
The application of domestic sewage sludge to agricultural land has become an acceptable method of
waste disposal and soil amendment. A great number of
studies have been published which document the
effects of sludge application on soil properties, nutrient availability and crop growth, heavy metal toxicity,
degradation of organic pollutants, and contamination
of surface and ground water. Studies of soil property
changes have selectively focused on nutrient enrichment and de®ciency, organic matter dynamics, chemical toxicities, microbial and enzymatic activity and
soil physical parameters (Metzger and Yaron, 1987;
Smith, 1991; Berti and Jacobs, 1996; Smith, 1996;
McBride et al., 1997). Sewage sludge application to
soil generally improves soil fertility by increasing the
soil organic matter, microbial activity and residual
nitrogen and by improving soil physical properties.
Reduced bulk density and increased porosity,
improved aggregate stability and enrichment of soil
organic carbon result generally in increased water
retention capacity and available water in coarse-textured soils and, in the long-term, in enhanced water
transmission properties as de®ned by improved
hydraulic conductivity and increased in®ltration.
However, it is necessary to apply sludge at large rates,
exceeding the maximum recommended level of N
application in manures, or at repeated low levels in
order to gain a signi®cant improvement of soil physical properties (Hall and Coker, 1983; Metzger and
Yaron, 1987; Smith, 1996). It is these high rates of
application that exceed crop N requirements which
may cause undesirable changes in soil chemical properties such as excessive soil acidi®cation from nitri®cation of the added ammonia, accumulation of
nitrates in sludge-treated pro®les and increased nitrate
leaching from susceptible loamy soils (Bergstrom and
Brink, 1986; Speirs and Frost, 1987; Chang et al.,
1988; Jansson et al., 1989; Powlesland and Frost,
1990).
Recent efforts for integrated soil quality assessment
recognize the need for reliable indicators of soil
productivity, environmental quality and plant/animal
health. In this study, a combination of physical, chemical and biological soil properties were used for the
evaluation of soil quality changes as a result of single
and repeated injection of liquid digested sludge in an
agricultural soil. The selected measurements comply
with the proposed selection criteria of soil quality
indicators in that they are sensitive to variations in
management, they de®ne major ecological processes
in soil and they re¯ect conditions as they actually exist
in the ®eld under a given management system (Doran
et al., 1996). Soil injection of sludge is widely practiced and signi®cantly reduces ammonia loss by volatilization, but leads to increased leaching of N as
compared to surface application (Williams and Hall,
1986; Smith, 1996). In this case, sludge was injected to
shallow depth for close proximity to crop roots in the
fall in order to minimize leaching losses (Shepherd,
1992; Smith, 1996). The speci®c objectives of this
study were the assessment of soil quality changes
caused by (a) repeated (long-term) liquid sludge injection at cumulative loadings that correspond to the
maximum annual recommended level of N application
in organic manures, (b) single sludge injection at rates
exceeding the maximum annual recommended level
of N application and (c) landscape position as compared to sludge injection effects.
2. Methods
2.1. Site description and sludge application
The experimental site is located in Lancaster county
NE, north of the city of Lincoln, NE, and is a terraced
dryland of east and west facing slopes meeting in a
grass waterway. Each slope was composed of an upper
and a lower terrace which, together with the waterway,
resulted in ®ve different sampling locations. The soil
type was Sharpsburg silty clay loam (®ne, montmorillonitic, mesic Typic Argiudoll).
The upper East terrace received anaerobicallydigested liquid sewage sludge from the NE Lincoln
sewage treatment plant by injection every three years
since 1982 at an estimated cumulative loading of
52 Mg haÿ1 of dry solids (ds) over a 12-year-period
for an average of 10.4 Mg ds haÿ1 (674 kg N haÿ1)
per injection which corresponds to 3.5 Mg ds haÿ1
yearÿ1 (225 kg N haÿ1 yearÿ1). In terms of N, this
is close to the maximum annual rate that is recommended for the application of organic manures (CEC,
1991; MAFF, 1991) in order to control nitrate contamination of groundwater in potentially susceptible
265
S. Stamatiadis et al. / Applied Soil Ecology 12 (1999) 263±272
areas. The site was cultivated to wheat without inorganic fertilizers in order to reduce excessive soil
nutrient loadings, the herbicide Roundup was used
to kill the wheat and the soil was disc-tilled prior to
sludge application. In addition, a 3.9-acre section of
the lower East terrace was reported to have received
458,514 L of sewage sludge (2.9% dry matter content,
8.4 Mg ds haÿ1 or 608 kg N haÿ1) for the ®rst time on
30 August, 1995. In terms of N, this rate is three times
higher than the recommended maximum annual application rate of organic manures (CEC, 1991; MAFF,
1991), but in terms of organic solids it is three times
lower than the suggested rates for a signi®cant
improvement of soil quality with respect to soil physical properties and organic matter content in sandy
loam soils (Smith, 1996). The sludge was applied by
injection to a depth of 20 cm below the soil surface in
rows of ca. 64 cm apart by a caterpillar track vehicle.
The chemical characteristics of the applied sludge are
presented in Table 1.
2.2. Soil sampling and analysis
An overview of the sampling scheme is given in
Table 2. Five random composite samples (0±30.5 cm
depth) were taken with a step-down Oak®eld probe
from each landscape position on 29 August and from
sludge application (row) and non-application (interrow) zones of the lower east terrace on 14 September,
1995. After mixing in a bucket, the samples were
sealed in plastic bags, placed in a portable cooler and
taken to the laboratory. Samples were sieved through a
2 mm sieve at ®eld moisture content prior to analysis.
Standard laboratory analysis of physical and chemical
properties of composite soil samples included gravimetric water content, bulk density (BD), nitrate and
ammonium nitrogen by extraction with 2 M KCl and
colorimetric determination with a ¯ow injection analyzer (Keeney and Nelson, 1982) followed by adjustment for 1 : 1 soil-water mixture from air-dried soil,
pH and electrical conductivity (EC) adjusted for 1 : 1
soil-water mixture, total C and N by dry combustion of
samples in an elemental analyzer (Schepers et al.,
1989), potentially mineralizable N (available N) by
the quantity of ammonium-N produced during incubation of soil samples for 1 week at 408C under
waterlogged conditions (Keeney, 1982). Measured
soil biological properties included basal soil respira-
Table 1
Chemical composition of liquid sewage sludge (pH 7) injected in
1.6 ha of the lower east terrace on 30 August, 1995
Component
Reported concentration
mg kgÿ1
dry kg haÿ1a
Total solids
Volatile solids
28900
15850
8398
4606
Total Nitrogen
Organic N
Ammonium N
Nitrate N
72457
45730
26740
6.8
Phosphorus
Sulfate
Iron
Potassium
10435
6207
11768
6290
Heavy metals and other
Arsenic
Cadmium
Chromium
Copper
Lead
Manganese
Mercury
Molybdenum
Nickel
Selenium
Silver
Zinc
9.6
5.9
43.4
1163
222
487
4.6
59.8
65.5
1.5
59.2
2292
608
384
224
0.06
88
52
99
53
0.08
0.05
0.36
9.8
1.9
4.1
0.04
0.50
0.55
0.01
0.50
19.25
a
Assuming 2.9% dry matter content and 290 538 L haÿ1 as the
reported sludge application rate.
tion by gas chromatographic analysis of headspace
CO2 after aerobic incubation of samples in sealed
1.9 L jars, net mineralization/ nitri®cation rates after
analysis of the incubated samples for ammonium- and
nitrate-N, biomass C by gas chromatographic analysis
of headspace CO2 of untreated and fumigated samples
with chloroform and biomass N by determination of
mineral nitrogen of the same samples. For the estimation of basal soil respiration, soil biomass, net mineralization and nitri®cation, non-fumigated soil samples
were incubated at 55% water-®lled pore space and
258C for 20 days. Biomass C and N was determined by
the fumigation/incubation method of Jenkinson as
described by Rice et al. (1996).
Replicated surface soil samples (0±7.6 cm depth)
were also taken from the lower east terrace on 14±15
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S. Stamatiadis et al. / Applied Soil Ecology 12 (1999) 263±272
Table 2
The soil sampling scheme (site, sampling depth, date) of the experimental area in order to test the effects of landscape position and sludge
injection
Site
Sludge injection
Sampling depth (cm) and site selection to test effect of
Landscape position
Repeated injection
29 August
Grass waterway
West upper terrace
West lower terrace
East upper terrace
East lower terrace
No
No
No
Repeated
No
No (inter-row)
Single (row)
30.5
30.5
30.5
30.5
September, 1995, 2 weeks after sludge injection. Soil
samples were collected with aluminium sampling
tubes (7.4 cm inside diam.) from three consecutive
rows and inter-rows in a perpendicular line so that the
distance between two consecutive samples was 32 cm.
Three additional top soil samples were taken from the
adjacent part of the terrace which had not been subjected to sludge injection (control samples). These
samples were analyzed for gravimetric water content,
bulk density, electrical conductivity, nitrate-N and pH
in the laboratory as described above. On-site water
in®ltration rate was measured within aluminum in®ltration rings (15 cm inside diameter) which were
inserted to a 7.6 cm soil depth. Soil respiration
(pre- and post-irrigation) was measured from the
headspace of in®ltration rings covered for 30 min
using Draeger tubes. Post-irrigation top soil samples
from within the irrigation rings were taken with the
sampling tubes and analyzed for soil bulk density and
water holding capacity (WHC). Further details of the
®eld soil quality procedures used are given by Sarrantonio et al. (1996).
2.3. Statistical analysis
Analysis of variance (ANOVA) was performed on
data obtained from replicated surface soil samples.
Sludge treatment was the independent factor of the
model in a completely randomized design. Neuman±
Keuls post hoc comparison of means was used at the
level of p < 0.05. Correlation coef®cients were computed between all microbial indices measured for 0±
30.5 cm depth by standard analytical procedures. All
Single injection
14 September
30.5
30.5
30.5
30.5
7.6
7.6/30.5
7.6/30.5
the employed procedures are reported in StatSoft
(1995).
3. Results and discussion
Bulk density, electrical conductivity, pH, nitrate and
ammonium N of the initial deeper soil samples (0±
30 cm) were similar in all terraces except those of the
upper east terrace which had repeatedly received
sludge since 1982. The upper east terrace had higher
soil conductivity, nitrate and ammonium levels and
lower pH than the other terraces (Table 3). Electrical
conductivity was positively related to nitrate concentration in all landscape positions except the waterway
(Table 3). Elemental analysis and anaerobic N mineralization showed a progressive increase of total C and
N and available N down the slope of the west side to
the waterway (Table 3). With the exception of biological indices involving microbial C, all other indices
of microbial activity followed a similar increasing
trend with lowest values in the upper west terrace.
Basal soil respiration, biomass N and its proportion to
total N (Nb : Nt) had the highest values in the grassed
waterway, the last two indices having values at least
two times higher than those of the west terraces. This
progressive increase in soil fertility was probably
caused by lateral leaching and surface erosion from
higher elevations. A possible similar pattern on the
east slope was obscured, and reversed, by sludge
application in the upper east terrace. Total C and N,
N availability and all biological indices had higher
values in the upper than the lower east terrace due to
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S. Stamatiadis et al. / Applied Soil Ecology 12 (1999) 263±272
Table 3
Soil quality changes as a result of landscape position and repeated sludge application
Soil quality indicator
Water-way
(grass)
Terrace position
Lower west
Upper west
Lower east
Upper easta
Physical
Soil bulk density (g/cm3)
1.38
1.43
1.49
1.42
1.41
Chemical
Soil EC1:1 (dS/m)
Soil pH
Soil NO3±N (kg NO3±N/ha 30.5 cm)
Soil NH4±N (kg NH4±N/ha 30.5 cm)
0.30
6.79
7.1
4.2
0.12
6.46
25.0
4.7
0.16
6.35
18.9
1.0
0.12
6.24
20.2
4.4
0.30
5.96
156.7
20.5
Total C (kg C/ha 30.5 cm)
Total N (kg N/ha 30.5 cm)
C/N Ratio
58467
5817
10.1
37920
4838
7.8
19 529
3 234
6.0
31 163
4 017
7.8
Biological
Biomass C (kg C/ha 30.5 cm)
Biomass N (kg N/ha 30.5 cm)
Biomass C : N
396
126.7
3.1
1299
45.6
28.5
794
43.7
18.2
218
30.6
7.1
Available N (kg NH4-N/ha 30.5 cm)b
Available N: Total C (mg/g)
Available N: Total N (mg/g)
113.2
1.9
19.5
60.0
1.6
12.4
38.4
2.0
11.9
36.4
1.2
9.1
34811
5011
6.9
1476
ÿ66.9e
75.3
2.2
15.0
Net mineralization (kg/ha 30.5 cm/day)
0±10 days
0±20 days
2.32
1.54
2.27
1.59
0.06
0.33
0.75
0.43
ÿ2.30
1.87
Net nitrification (kg/ha 30.5 cm/day)
0±10 days
0±20 days
2.64
1.73
2.67
1.82
0.09
0.37
1.12
0.64
ÿ0.30
2.86
Respiration (kg CO2±C/ha 30.5 cm/day)c
0±10 days
10±20 days
0±20 days
4.76
3.18
3.97
2.71
1.37
2.04
3.19
1.94
2.57
1.76
1.08
1.42
2.81
1.32
2.07
3.4
0.9
1.6
4.1
0.8
3.2
0.7
1.4
6.5
4.2
Biomass C: total C, %
Biomass N: total N, %
Specific respiratory activityd
0.7
2.2
10.0
1.4
a
Injected with sewage sludge every 3 years since 1982.
NH4±N released during anaerobic incubation for 1 week at 408C.
c
2.25 cm depth.
d
qCO2 (mg CO2-C gÿ1 biomass C dayÿ1).
e
Error due to presence of readily decomposable organic material resulting from sludge injection.
Values represent single measurements of composite samples (0.30.5 cm depth, n 5) taken on 29 August, 1995.
b
long-term sludge application (Table 3). The higher
ratio of available N: total C in the soil of repeated
sludge injection is indicative of the presence of readily
decomposable organic material.
The effects of the single sludge injection at the
lower east terrace were similar to those of repeated
sludge injection. The treated soil (sludge rows) had
greater organic matter content, microbial activity,
268
S. Stamatiadis et al. / Applied Soil Ecology 12 (1999) 263±272
Table 4
Effects of recent sludge injection on indicators of soil quality
Soil quality indicator
Area of sludge injection
Application row (sludge)
Physical
Soil bulk density (g/cm3)
Chemical
EC1:1 (dS/m)
Soil pH
Soil NO3±N (kg NO3±N/ha 30.5 cm)
Soil NH4±N (kg NH4±N/ha 30.5 cm)
1.36
1.35
1.0
0.37
6.28
172.2
67.2
0.10
6.71
8.9
3.0
3.7
0.9
19.4
22.4
Total C (kg C/ha 30.5 cm)
Total N (kg N/ha 30.5 cm)
20312
3826
Biological
Biomass C (kg C/ha 30.5 cm)
Biomass N (kg N/ha 30.5 cm)
ÿ205b
ÿ69.0b
Available N (kg NH4±N/ha 30.5 cm)a
Available N: total C (mg/g)
Available N: total N (mg/g)
Net mineralization (kg N/ha 30.5 cm/day)
0±10 days
0±20 days
Inter-row (no-sludge)
Ratio
Sludge/no-sludge
66.5
3.3
17
17282
2724
1.2
1.4
138
22.7
18.0
1.0
7
3.7
3.3
2.4
8.18
8.00
0.29
0.32
28.2
25.0
Net nitrification (kg NO3±N/ha 30.5 cm/day)
0±10 days
0±20 days
14.57
11.26
0.50
0.46
29.1
24.5
Respiration (kg CO2-C/ha 30.5 cm/day)
0±10 days
10±20 days
0±20 days
34.8
36.9
35.9
16.8
12.3
14.6
2.1
3.0
2.5
a
NH4±N released during anaerobic incubation for 1 week at 408C.
Error due to presence of readily decomposable organic material resulting from sludge injection.
Values represent single measurements of composite samples (0±30.5 cm depth, n 5) taken on 14 September, 2 weeks after sludge
application.
b
available N, mineral N and electrical conductivity and
decreased pH relative to the untreated soil of the interrows, 2 weeks after sludge injection (Table 4).
Digested sludge injection at a rate of 608 kg N haÿ1
was three times higher than the recommended maximum application of organic manures (160 or 210 kg
N haÿ1 yearÿ1; CEC, 1991), four times higher than the
range of 100±160 kg N/ha estimated to be the `breakpoint' which prevents nitrate leaching for cereals
(Bergstrom and Brink, 1986; Jansson et al., 1989)
and, based on calculations of Powlesland and Frost
(1990), may be expected to increase groundwater
concentration by approx. 9 ppm NO3-N. Two weeks
after injection, the majority (72%) of the ammoniumN contained in sludge was converted to soil nitrate-N
whose concentration raised to levels that were two
times higher than suf®ciency levels for corn during
early growing season (20±25 ppm, Bundy and Meisinger, 1994, p. 958), which equated to 80±
100 kg haÿ1 in the top 30 cm. Suf®ciency levels for
manured soil are even lower at about 16 ppm or less
that equate to